The Earth's climate has changed many times during the planet's history, with events ranging from ice ages to long periods of warmth. Beginning late in the 18th century, human activities associated with the Industrial Revolution have also changed the composition of the atmosphere and therefore very likely are influencing the Earth's climate.
For over the past 200 years, the burning of fossil fuels, such as coal and oil, and deforestation, have caused the concentrations of heat-trapping "greenhouse gases" to increase significantly in our atmosphere. Greenhouse gases are necessary to life as we know it, because they keep the planet's surface warmer than it otherwise would be. But, as the concentrations of these gases continue to increase in the atmosphere, the Earth's temperature is climbing above past levels.
Climate change affects people, plants, and animals. Scientists are working to better understand future climate change and how the effects will vary by region and over time. Scientists have observed that some changes are already occurring. Observed effects include sea level rise, shrinking glaciers, changes in the range and distribution of plants and animals, trees blooming earlier, lengthening of growing seasons, ice on rivers and lakes freezing later and breaking up earlier, and thawing of permafrost. Another key issue being studied is how societies and the Earth's environment will adapt to or cope with climate change.
Primary Source Media's microfilm series documents the U.S. response to the threat posed by climatic change and global warming. The research behind the studies, reports, and analyses represents an exhaustive review of the facts, causes, and economic and political implications of a phenomenon that threatens every region of the world.